Electric switch



Nov. 29, 1 932.

R. KELLER 1,889,479

ELECTRIC SWITCH 2 Sheets-Sheet 1 Filed May 5, 1928 Fig. 3

Nov. 29, 1932. KELLER 1,889,479

ELECTRIC SWITCH Filed May 3, 1928 2 Sheets-Sheet 2 I) l l 1 P m F lg4 +ka H -L IX.

Patented Nov. 29, 1932 UNITED STATES PATENT OFFICE ROBERT KELLER, OFENNETBADEN, SWITZERLAND, ASSIGNOR TO AKTIENGESELLSCHAFT BROWN, BOVERIAND (HE, 0F BADEN, SWITZERLAND ELECTRIC SWITCH Application filed May 3,1928, Serial No. 274,898, and in Switzerland May 7, 1927.

The release of ordinary electric switches is usually effected by causingthe force of a spring or weight to act on the movable switch contact,which force is made inoperative by lockin means durin normal workin andis b 23 D released on the current limit being exceeded by the saidlocking means being released. The switch is then immediately opened.although this takes place only after these moving masses have beenaccelerated. In order to cause the release of the switch to take placemore rapidly, it would suiiice to increase the force of the spring(weights cannot suitably be used for quick-acting switches, owing to themasses to be accelerated). A spring of increased strength, however,entails a greater friction on the releasing mechanism, which againdemands an increase in the releasing force. For this reason a limit issoon reached, beyond which for practical and economical reasons theforce of the spring for the release motion may not be increased. As,however, in certain cases a particularly rapid release of the switch isrequired, many switches have been made for shortening the time requiredto release the switch.

According to the present invention a new solution for this problem issuggested, according to which in breaking the circuit the movablecontact, besides being subjected to the said spring force, is acted onindependently of the latter by a further additional force which istransmitted mechanically to it and is also caused to act in dependenceon the magni tude of the current or of the increase in current.

This new means for accelerating the circuit breaking process may beembodied in a great number of constructional forms, three 0f which shallnow be explained with reference to the accompanying drawings, in whichFig. 1 represents the diagram of connections of a quick-acting switch,Figs. 2 and 3 two different constructional forms of a part of the switchand Figs. 4 and 5 a further modification, such as is suitable forreleasing reverse current. Fig. 6 shows a modification of the system ofFig. 1. In this switch according to Fig. 1 two releasing forces, a triprelease and an electro-dynamic release, acting on the movable switchmember a which, when closed, rests against the fixed switch contactbrush 5. As one force need not be equal to the other force nor actsynchronously with it, they are not rigidly but elastically coupledtogether. For this reason the shaft of the switch is composed of twoparts 0 and d. The movable switch member a is mounted rigidly on thepart 0 of the shaft and is connected to the other part d of the same bymeans of a free-wheel coupling or by a similarly acting spring 6 whichis fixed to a pin 8 in the switch member a. On the part d of the shaftis also mounted a driving lever r. The releasing spring f of the tripgear is attached to the lever g mounted on the part (i of the shaft,which lever is held in the switched in position by the detent k. The

latter is under the influence of the maximum current magnet a. On theother side in the magnetic field of the coil m lies the short circuitwinding 70 having the form of a rotary coil, which acts under variationsin the current and is mounted on the part c of the switch shaft. Inorder to prevent the switch opening unintentionally when a non-inductivemaximum load is switched on, the electric coupling 6 (or the free-wheelmechanism) between the shafts c and d may be made capable of beinglocked at will.

As will be seen from Fig. 2, the short circuit winding referred to abovelies in the air gap Z of a three-limbed magnet core n which is energizedby the main current winding m, which air gap is concentric with therotary shaft 0 of the rotating coil 70. When there is a rapid increasein the current, a short circuit current proportional to the change inthe field is induced in the rotary coil by transformer action, whichshort circuit current acts in opposition to the change in the field. As,however, two sides of the coil in are cut by the lines of forceindicated by broken lines in the air gap Z of the magnet n, anelectro-dynamic force acting in the direction of the arrows in fulllines is exerted on its outer conductors of the coil, through which theshort-circuit current flows, which force is the greater the more rapidthe increase in the current in the coil m and the greater its absolutevalue. For increasing the eifect the two magnetic circuits, one of whichserves for the transformer induction of the short circuit current andthe other for producing the torque in the coil, might be separated fromone another (Figs. 4 and 5) since the short circuit winding 70 damps thefield produced by the primary coil m.

On a short-circuit occurring in the circuit of the switch a, I), theeffect is such that, owing to the momentary increase in current, thecoil is has a torque imparted to it and lifts the switch lever a fromthe brush Z). At the same time the detent It will have been released bythe excess current so that the spring f acting on the lever g, theshaft" d and the coupling spring 6 or on the driving mechanism 1', s,also exerts a disconnecting force in the same direction as the coil 70on the switch lever a, before the short circuit cur- 'itact being brokenmay be extinguished in any of the usual ways, thus forming no part ofthe present invention.

In many cases it is admissible and even desirable that the coil 76 shallexert, even on ycurrent increases occurring below the maximum point,atorque which reduces the contact pressure between a and I) or evencauses the switch to open for a short time. In this case the force ofthe spring e causes the smswitch to close again each time before the arebetween the switch contacts is broken. It is also possible to make thearrangement such,

that the increase in current only produces a torque in the coil is whenthe absolute value ;of the current has exceeded a definite amount.

According to Fig. 3 the iron circuit for the coil 70 may be divided intotwo separate circuits n and a, each of which is energized by its ownenergizing coil m and m and :1which are arranged on either side of thecoil shaft 0, say symmetrical to the same.

Instead of the electro-dynamic effect of the current or the increase incurrent being utilized directly for opening the switch, it can fiQibeutilized indirectly for releasing any other force effect for actin onthe movable switch contact, for instance for opening or closing thevalve of a compressed air motor operating the switch arm or for couplingthe switch arm to a continuously rotating fly-wheel or '2 and 3, say asshown in Figs. 4 and 5.

ed and disconnected.

Fig. 4 shows in a constructional form of switch operating gear whichacts only with reverse current, the magnet core for the transformerinduction of the driving coil which is coupled to the shaft 0 of theswitch in elevation, and the magnetic circuit for producing the motionof the coil is in section, and Fig. 5 shows a plan view of the samearrangement, the magnet core first referred to being in section and themagnetic circuit for producing the motion of the coil is in elevation.The coil m, through which the main current flows, is interlinked withthe short circuit winding is by the laminated iron core a which in thiscase has no air gap. The longitudinal sides of the coil 70 lie in theair gap Z of a stationarv iron circuitcomposed of two parts 0 and pwhich is energized from an I external source of the winding 9. The ironcircuit 0, go is so arranged that the coil is when at rest, the switcha, 6 being closed, lies approximately at the edge of the air gap Z. Thetwo magnetic circuits are furthermore so energized that, on a reversecurrent occurring in the main circuit, to which the switch a, b and thecoil m belong, the coil in may be drawn into the air gap Z while in thecase of a normal current it will be repelled out of the said air gap.The arrows shown in Figs. 1- and 5 apply to the former case. Hence, on areverse current occurring the switch contact a (Fig. 1) will be operatedin the opening direction, on an increase in the reverse currentoccurring. On the reverse current dying down again, before havingreached the necessary height for releasing the detent k, the

coil 76 will turn in the reverse direction and even when the normalcurrent has again died down. If necessary it can be returned by aseparate-returning spring into-the ready position. e

v A particular advantage of this arrangement is that the switch a, b canbe closed at full load, without there being any danger of its beingreleased again through the sudden considerable change in current, asthrough the increase in current in the forward direction, the coil ismoved in the closing direction of the switch.

The maximum current release f, g, i, h of the switch a, b is of courseintended to act with both directions of current, in order to preventoverloads and the burning out of the machines or apparatus to beprotected. The combination last described is particularly suitable forrectifier plants. In such plants it will act selectively in the case ofbackignitions, that is only that rectifier will be disconnected, inwhich a heavy back ignition is occurring. In the case of lighter backignitions in which the reverse current does not reach the maximumcurrent limit, no final disconnection will take place at all, the switchbeing opened only during the increase in the reverse current andimmediately closed again on the reverse current decreasing. Such anaction of the arrangement is required in practice in connection withrectifier plants.

The transformer transmission of a changing current to the rotary coilcan also be effected by means of a transformer as shown in Fig. 6. Inthis case the rotary coil 70 which is coupled to the shaft 0 of theswitch is fed by means of the transformer 23. As the voltage willsuddenly drop on a short circuit occurring, a transformer 11 may be usedfor energizing the magnetic field having the motor action, in front ofthe primary to which a resistance a may be inserted and the secondary ofwhich feeds the magnet winding 9. Such a way of operating the switch a,I) may be so arranged as to act only in the case of reverse current.

WVhat I claim is:

1. A switch adapted for quick release including a fixed contact, amovable switch member carrying a movable contact, resilient meanstending to force apart said contacts, a

locking device holding said contacts together against the force of thesaid resilient means and additional means independent of said lockingdevice and tending to force apart said contacts in dependence upon therate of change of current through said contacts.

2. A device as claimed in claim 1, wherein said resilient means iscoupled non-rigidly with said switch member and said additional means iscoupled rigidly to said switch member.

3. A device as claimed in claim 1, wherein said additional meanscomprises a rotary coil coupled to the movable switch member and locatedin the air gap of a magnetic circuit.

L. A device as claimed in claim 1, said additional means comprising arotary coil coupled to the movable switch member and located in the airgap of a magnetic circuit and a coil in series with said current toproduce flux in said magnetic circuit.

5. A device as claimed in claim 1, said additional means comprising arotary coil coupled to the movable switch member and located in the airgap of a magnetic circuit, and a coil in series with said current toproduce flux in said magnetic circuit, which is magnetically linked withthe rotary coil so that the coil energized by the current through theswitch contacts induces current in the rotary coil.

6. A device as claimed in claim 1, said additional means comprising arotary coil coupled to the movable switch member and located in the airgap of a magnetic circuit, and a coil in series with said current toproduce flux in said magnetic circuit, which is magnetically linked withthe rotary coil so that the coil energized by the current through theswitch contacts induces current in the rotary coil, which is shortcircuited on itself.

7. A device as claimed in claim 1, said additional means comprising arotary coil coupled to the movable switch member and located in the airgap of a magnetic circuit, and a coil in series with said current toproduce flux in said magnetic circuit, which is magnetically linked withthe rotary coil so that the coil energized by the current through theswitch contacts induces current in the rotary coil, which is shortcircuited on itself and consists of a single turn.

8. A device as claimed in claim 1, wherein said additional meanscomprises a rotary coil coupled to the movable switch member and locatedin the air gap of amagnetic circuit, said magnetic circuit beingmagnetically linked with the rotary coil so that change of flux in saidmagnetic circuit tends to rotate the rotary coil.

9. A device as claimed in claim 1, wherein said additional meanscomprises a rotary coil coupled to the movable switch member and locatedin the air gap of a magnetic circuit, said magnetic circuit beingmagnetically linked with the rotary coil so that change of flux in saidmagnetic circuit tends to rotate the rotary coil, and said magneticcircuit is arranged symmetrically with respect to the rotary coil.

In testimony whereof I have signed my name to this specification.

ROBERT KELLER.

